Harden API input validation, error handling, and optimistic rollbacks

Add try/catch around `request.json()` in all POST routes to return a
400 instead of crashing on malformed bodies. Validate `type` as a
strict `"movie" | "tv"` enum in search, discover, import, and resolve
routes. Validate `tmdbId` as a positive integer. Add a
`SORT_BY_PATTERN` regex and page-range check (1–500) to the discover
route. Wrap all outbound TMDB calls in try/catch and return 502 on
failure so clients get a structured error rather than an unhandled
rejection.

Fix optimistic-update rollbacks in `use-title-actions`: capture
`prevStatus` and `prevWatches` before each mutation and restore both
atoms in the catch block for catchUp, handleMarkSeason,
handleUnmarkSeason, and single-episode toggle.

Fix a bug in `getContinueWatchingFeed` where the watchDateMap could
hold a stale date for episodes watched more than once; the map now
keeps the most-recent `watchedAt` per episode.

lib/services/metadata.ts

@@ -559,13 +559,29 @@ export async function getTitleWithChildren(id: string): Promise<{
   let titleSeasons: Season[] = [];
 
   if (title.type === "tv") {
-    const seasonRows = db
+    let seasonRows = db
       .select()
       .from(seasons)
       .where(eq(seasons.titleId, title.id))
       .orderBy(seasons.seasonNumber)
       .all();
 
+    // Retry hydration when a TV title exists but no seasons were stored.
+    if (seasonRows.length === 0) {
+      try {
+        const show = await getTvDetails(title.tmdbId);
+        await refreshTvChildren(id, title.tmdbId, show.number_of_seasons);
+        seasonRows = db
+          .select()
+          .from(seasons)
+          .where(eq(seasons.titleId, title.id))
+          .orderBy(seasons.seasonNumber)
+          .all();
+      } catch (err) {
+        log.debug(`Failed to backfill missing seasons for title ${id}:`, err);
+      }
+    }
+
     // Batch fetch all episodes for all seasons (1 query)
     const seasonIds = seasonRows.map((s) => s.id);
     const allEps =